88 
Psyche 
[March 
habitats, with D. introita and D. acadia mostly in woods-edges and 
fields and the other five species confined to woods. 
Finally, it should be emphasized that few, if any, Valley mesos- 
tenines show definite association with an individual plant species 
or plant community. Mesostenines generally are so versatile in 
host selection that each one may occur in almost any physically 
suitable environment with appropriate vegetation structure, irre- 
spective of the taxonomic composition of the local flora. 
Diversity 
The first component of diversity is richness or number of taxa 
inhabiting a particular region. In this study, I have reported 18 
genera and 35 species of Mesostenini from the Valley. As already 
noted, that number agrees rather well with faunas of other arid 
Middle and South American localities, such as the Peruvian Coastal 
Desert, with 10 genera and 31 species, or the Argentine Subandino, 
with 10 genera and 33 species. All these habitats are too xerother- 
mic for optimum mesostenine radiation and contain only a mod- 
erate amount of niche space in their simply stratified herbaceous 
and shrub or herbaceous, shrub, and small tree layers. On the 
other hand, humid, multilayered subtropical and tropical forests 
may have seven or eight times the number of mesostenine species 
present in even nearby deserts. For example, the north Argentine 
wet forests, Selva Tucumano-Boliviana and Selva Misionera, of 
which the former in places practically interdigitates with the Suban- 
dino, have yielded in 10 years of net and Malaise collecting 40 
genera and 237 species of mesostenines. I do not yet have similar 
data for the northeast Mexican wet forests, which extend along the 
Sierra Madre Oriental to within 200 km. of the Lower Rio Grande 
Valley, but the fact that five days’ hand collecting in a humid ravine 
at Cola de Caballo near Monterrey (31 May-4 June 1974) produced 
12 mesostenine genera (Glodianus, Lymeon, Rhinium, Toechory- 
chus, Cryptanura, Bicristella, Polycyrtus, Messatoporus, Cestrus, 
Joppidium, Listrognathus, and Baltazaria ) suggests that the dif- 
ference in mesostenine richness between these localities and south 
Texas eventually will prove similar to that already documented be- 
tween the Argentine Subandino and its nearby subtropical forests. 
A second component of diversity is the apportionment of indi- 
